1. Field of the Invention
The invention relates to a pressure regulating valve for a common-rail fuel injection system for internal combustion engines, for regulating the pressure in the common rail and having a pistonlike valve member guided axially displaceably in a bore, which valve member acts on a closing element which can be pressed against a valve seat, and the valve member forms an armature of an electromagnet that can be supplied with current. Electromagnets with movable armatures are furthermore used as actuators in many kinds of applications.
2. Description of the Prior Art
Pressure regulating valves are known in manifold versions, including pressure regulating valves serving to regulate the pressure in a common rail, with which it communicates via an inlet. The pressure regulating valve has a pistonlike valve member, guided axially displaceably in a bore, that can move counter to a force which is exerted on the valve member preferably by the current in the electromagnet. The force acts in the closing direction, so that the valve member presses against a closing element of the pressure regulating valve and is pressed against a valve seat. The valve member forms an armature of an electromagnet, which can be supplied with current for controlling the force.
Supplying current via the valve member causes the closing element to press against the valve seat with a defined force, and the closing element is lifted from the valve seat by the pressure in the common rail acting on it, if the force generated by the pressure exceeds the closing force that is exerted on the closing element via the valve member. In that case, fuel flows out of the common rail through the inlet into a relief chamber via the opened pressure regulating valve.
When a higher pressure is to be established in the common rail, the current in the electromagnet is increased, so that the closing force is increased, and thus the closing element does not lift from the valve seat until a higher pressure is established in the common rail, whereupon fuel can flow out of the common rail into the relief chamber.
If no current is supplied to the electromagnet, the valve member is pressed against the valve seat only by its own weight. Moreover, a mechanical spring can be installed, which with its spring force presses the valve member against the closing element and the valve seat. This force is independent of the current supply to the electromagnet.
If a functional problem in supplying current occurs in the electromagnet, for instance from loosening of the corresponding plug, causing a failure of the electromagnetic closing force, then fuel at low pressure can penetrate the relief chamber and make an injection impossible. In that case the vehicle can no longer be driven.
If an additional pressure is generated by means of a mechanical spring, then emergency travel is indeed possible, but the spring force acting on the valve member cannot be regulated.